An internal combustion engine system may include a compound turbocharger system. A compound turbocharger system includes a pair of turbochargers arranged with a pair of turbines fluidly connected in series, and a pair of compressors fluidly connected in series. Each turbine is mechanically coupled to a compressor, to drive the compressors with engine exhaust. The compressors, in turn, pressurize engine intake air that is supplied to the engine cylinders.
Such an engine system may also include an exhaust gas recirculation (EGR) system to assist in controlling the generation of undesirable pollutant gases and particulate matter. EGR systems recirculate a portion of engine exhaust into the incoming engine intake air thereby reducing the concentration of oxygen in the cylinders, which in turn lowers the peak in-cylinder combustion temperatures and exhaust temperature. Accordingly, EGR systems reduce the formation of certain pollutants, e.g., nitrous oxides (NOx), generally produced at higher combustion temperatures. Moreover, recirculating the exhaust gases promotes the combustion of unburned hydrocarbons in the exhaust gases, thus further reducing engine emissions. However, providing EGR reduces engine efficiency.
One example of an engine system having an EGR system can be found in U.S. Pat. No. 9,051,903, which discloses an EGR system that recirculates exhaust gas from one or two exhaust manifolds into the intake manifold. While the EGR system described by the '903 patent may be beneficial, the efficiency of such an engine system may be improved.
The engine system of the present disclosure may solve one or more of the problems set forth above and/or other problems in the art. The current scope of the disclosure, however, is defined by the attached claims and not by the ability to solve any specific problem.